Bonding with a compliant medium

ABSTRACT

A plurality of independently displaceable pins are employed to apply bonding pressure to a compliant medium at widely spaced bonding sites. The pins permit compensation for workpiece irregularities between the bonding sites such as substrate waviness, warpage, lack of parallelism, etc., while the compliant medium compensates for localized workpiece irregularities such as variations in the thickness of leads and/or land areas.

United States Patent 1151 3,669,333

Coucoulas 1 June 13, 1972 541 BONDING WITH A COMPLIANT 2,524,932 10 1950Schulman 156/323 x MEDIUM 2,710,046 6/1955 Markus et al. .....156/325 x3,146,524 9 1964 Tetzlofi ..29/407 Inventor: Alexander Coucoulas,Bridsewawr 3,284,962 11/1966 Hottetal ..269/310x Township, Somerset y.3,379,595 4/1968 Bracey, Jr. ..156/323 x 3,507,733 4/1970 Davidson..156/323x [73] Ass'gnee' n g zg f'mj Cmpflny lncorpm'ed 3,520,0557/1970 .lannett ..269/21X 2,524,932 10/1950 Schulman ..156/323 [22]Filed: Feb. 2, 1970 Primary Examiner-John F. Campbell [21 1 App. 7473Assistant Examiner-Robert J. Craig Related U 8 Application DataAttorney-W. M. Kain, R. P. Miller and R. C. Winter [63]Continuation-impart of Ser. No. 651,411, July 6, [57] ABSTRACT 1967' Aplurality of independently displaceable pins are employed to applybonding pressure to a compliant medium at widely 52 1 us. c1 ..22s/3,29/471.1, 156/323, Spaced bonding Sim The pins pemm compensation forwot, 228/4 269/310 piece irregularities between the bonding sites suchas substrate [5|] ..B23k 21/00 waviness, warpage lack of'parauelism, etcu the 2 3| 317; 228/3 pliant medium compensates for localized workpieceirregu- 228/4, 156/323, 73 lan'ties such as variations in the thicknessof leads and/or land areas. [56] References Cited 12 Claims, 20 DrawingFigures UNITED STATES PATENTS 593,879 11/1897 Du Brul .;....2 9/31oPATENTEDJHN 13 m2 3. 669 333 sum 20! 5 PATENT ED 1 3 9 2 SHEET 5 OF 5 1BONDING WITH A COMPLIANT MEDIUM CROSS-REFERENCES TO RELATED APPLICATIONSBACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates generally to bonding and, more particularly, it relates to thebonding of two or more first workpieces to a second workpiece. The firstworkpieces may comprise two or more small wires, integrated circuitdevices, small, brittle crystals, or beam-lead transistor or integratedcircuit devices. The second workpiece may comprise a thinfllm orintegrated circuit formed on an insulating substrate, a printed circuitboard, or the like. The invention has application to the bonding ofworkpieces other than the abovedescribed types, but since it isparticularly adapted for such workpieces it will be described withreference thereto.

In simultaneously bonding a plurality of leads, workpiece irregularitiesrender reliable bonding difficult. For example, if leads are positionedon a substrate and eight of them are exactly the same size but two are10-20 percent smaller, a flat ram or bonding tip will make only eightbonds. Or, if enough pressure is applied to contact all 10 leads, eightof them will be deformed too much, resulting in a weak or killed" bond.In another case, the leads may be of exactly equal size, but thethickness of the metallic land areas on the substrates may vary, thethickness of the substrate may vary, or the bonding tip may be worn ormisaligned, sufficiently to prevent the energy source (ram or ultrasonicbonding tip) from making an energy-transmitting couple with each lead.Thus, the problem is not bonding leads simultaneously per se, but ratherreliably bonding every lead in a group, simultaneously, every time. Evenwith the most sophisticated quality control techniques and the closesttolerances obtainable, simultaneous bonding of a number of leads has notproven to be reliable or economic.

In addition, as circuits have become more and more complicated, it hasbecome necessary to bond a plurality of devices such as beam-leaddevices to a circuit. As will be appreciated, it is highly desirable tobond all of these beam-lead devices in a single bonding operation. As aresult, a great deal of effort has been expended in attempting todevelop so called multichip bonding techniques. As the substrate of thecircuit may be non-parallel, i.e., the two major surfaces of thesubstrate may not be parallel, the substrate may be warped or wavey, orthe bonding tool may not be parallel, the bonding tool may applyexcessive force to one area of the substrate and insufficient force toanother area thereby fracturing the sub strate and/or making unreliablebonds. Accordingly, it is extremely difficult to reliably bond at widelyspaced bonding sites without compensating for such workpieceirregularities. Therefore, multichip bonding must not only solve all ofthe above-mentioned problems, but as relatively large areas are involveddamage to the substrate of the circuit must also be" avoided. This istrue of lead bonding at widely spaced bonding sites as well as multichipbonding.

2. Description of the Prior Art The techniques of ultrasonic andthermocompression bonding, particularly as applied to bonding leads tosubstrates, are well known in the art. In the field of electric weldingthe use of flexible electrodes and electrodes mounted on resilientsupports was proposed many years ago (see, for example, U. S. Pat. No.475,191 and No. 2,226,424).

Gang welding at several spaced welding stations was proposed in U. S.Pat No. 3,053,125. The patentees place the workpieces on movablesupports located under each bonding head, then move the support up toclamp the workpieces in place. The welding heads are located on a longrod at points of antinodal vibration. The rod is connected to anultrasonic transducer, and a single application of ultrasonic energywill make a single bond at each welding station. There is no known priorart utilizing a compliant medium in connection with ultrasonic orthermocompression bonding.

There has been proposed, however, a method of soldering connections to aplurality of flexible cables at one time. In this method, the portionsof the conductors desired to be bonded are coated with solder, and thecable assembly is laid over the contact elements, which rest on a rigidsupport. A Teflon (trademark) sheet is laid over the cable insulationand a quartz plate is laid on top of the sheet. A tungsten halogen lampprovides infrared heat energy which passes through the quartz, Teflonand insulation (all of these members being more or less transparent toinfrared radiation) which melts the solder and makes the bond. Thequartz acts as a heat sink and a clamp (see Broyer and Mammel: FlexCable Interconnections Mass Bonded With Infrared Proceedings, NEP/CON'67, July 1967).

OBJECTS OF THE INVENTION It is a general object of the present inventionto provide an apparatus for bonding metallic surfaces of workpieces.

A further object of the present invention is to provide an apparatus forbonding a plurality of workpieces to asubstrate simultaneously.

Yet another object of the invention is to provide an apparatus forsimultaneously bonding the leads of a plurality of beam-leaded devicesto metallic land areas of a substrate.

Still another object of the invention is to provide an apparatus forbonding the leads of a plurality of beam-lead devices to a substratewhile compensating for workpiece irregularities.

Another object of the invention is to provide a novel jig assembly forbonding at widely spaced areas of a substrate.

Various other objects and advantages of the invention will become clearfrom the following summary and detailed description thereof.

SUMMARY OF THE INVENTION In essence, the present invention is based, atleast in part, on

the discovery that the use of a compliant or deformable medium toholdthe workpieces has many significant advantages in bonding, and thatsufficient thermal and/or mechanical energy can be transmitted throughor absorbed by such a medium to effect a good bond between theworkpieces.

Understanding of the invention will be facilitated by considering thetransmission of energy through a compliant or deformable medium. 1

While a compliant medium may be easy or difiicult to deform, it willtransmit pressure while absorbing energy. Thus, if a 100 pound weight isplace on a 1 inch cube of steel resting on a rigid support, the steelwill deform very little and the pressure on the support will be 100 psi.If the cube is made of hard rubber rather than steel, the deformationwill be much greater but the pressure on the support will still be 100psi. The energy of deformation in each instance is represented by thedistance movedby the weight lower than one inch. If the weight squeezedthe rubber to a height of inch, for example, the energy of deformationwould be (l "36) X 1/12 X 100 2.09 foot pounds. The potential energyrepresented by the 100 psi pressure on the support is still available toperform work.

If a second piece of deformable material is placed between the rigidsupport and the hard rubber cube, there will be a relative deformationof both substrates. Naturally, if the second material is also a cube ofhard rubber, the deformation of both pieces will be equal. Thedistribution of deformation between two dissimilar materials can bedetermined from the stress-strain curve of each material. That is, undera given stress, the strain of each material can be read directly fromthe curve. This is not limited by the points on the curves where themode of deformation changes from elastic to plastic (i.e., the

elastic limit). Thus, if a cube of material A is resting on a cube ofmaterial B which is, in turn, resting on a rigid support, and a 100pound weight is placed on cube A, the deformation of both may be elasticor plastic, or one may deform elastically while the other deformsplastically. In any case, the behavior of the respective materials canbe predicted from the stressstrain curve.

From the foregoing it is believed to be clear that under the influenceof pressure (i.e., mechanical energy) alone, one compliant (ordeformable) material can deform another deformable material.

The above discussion was concerned only with two cubes of the same size.If, in place of the 1 inch cube of material B, there is substituted twoV4 X A X l in. bars, the pressure on each bar will be 200 psi since thetotal pressure must in this instance be transmitted through in ofsurface. However, the deformation of material A will be considerablydifferent. With two equal cubes, both materials will tend to flatten,i.e., bulge outwardly on the sides, where they are not confined. If cubeA is resting on the two bars presenting an aggregate surface area of iin*, however, cube A will tend to deform downwardly, between or aroundthe bars. If, now, in place of cube A there is substituted a round rodof k in. diameter laid across the two bars, the stress-strain situationchanges radically. The area of contact between rod A and bars B is verysmall, so the stress (for the same IOO-pound weight) must be very large;This will cause an appropriate increase in the strain (deformation) ofboth materials. In other words, it is the stress at the interface,rather than the total force applied, which determines the deformation ofboth materials. Thus, by controlling the geometry of the two materials,a relatively small force can be made to cause a relatively largedeformation.

The mode and amount of deformation will also be radically influenced bythe application of thermal energy. This is also predictable from thestress-strain curve of the chosen materials at the specifiedtemperature.

In summary, the following factors can be used to control relativedeformation between the two bodies: (1) Selection of materials; (2)Total mechanical energy applied; (3) Geometry of the pieces; and (4)Application of heat.

The foregoing principles are directly applicable to the presentinvention, and a simple example will illustrate this. It is desired tobond a l6-lead beam-lead device (gold leads) to the gold land areas on asubstrate, using a ram pressure of 30 pounds at 400 C. The leads arematerial B, the land areas are the rigid support, and material A is whatis referred to herein as the compliant medium. To select a suitablecompliant medium, the stress-strain curve of gold at 400 C is plotted,preferably on a log-log plot where the yield point, is on the ordinate,and the slope of the curve is the strain hardening index. From thisplot, the stress necessary to achieve any degree of deformation of thegold can be determined. If 50 percent deformation (0,) of the lead isdesired, a particular stress, 0-,, will achieve it. If the compliantmedium is twice as thick as the lead, it will only deform 25 percent indeforming the lead 50 percent, so any material having a stress-straincurve which deforms 25 percent (6 at the desired stress (0-,) is asuitable medium. In this instance, 2024 aluminum is a satisfactorymedium. Having selected a medium, the geometry is considered. Thesubstrate rests on an anvil, the device is placed thereon, and thecompliant aluminum frame, covering only the leads, is laid thereover.The heated ram is brought down under a 30 pound (absolute) load. Thepressure at the ramaluminum interface is found to be about 2000 psi.This is below the yield point of this alloy at 400 C. However, theavailable pressure at the aluminum-lead interface, which is a muchsmaller area, is in excess of 100,000 psi, which is greatly above theyield point of both metals, so that deformation occurs. When thealuminum has deformed around the leads and touches the substrate (asdescribed in detail hereinbelow), the area of contact increases (and thepressure decreases) until it is the same as the area of the ram-aluminuminterface, i.e., the pressure drops to about 2000 psi, and defonnationstops.

As will be appreciated, the compliant .medium by deforming around eachlead compensates for variations in lead thickness, variations in landarea thickness, local variations in substrate thickness, and localvariations in parallelism between the substrate and the heated ram topermit the simultaneous multiple lead bonding. However, when leads arebonded at widely spaced bonding sites or a plurality of beam-leaddevices are bonded simultaneously, the compliant medium may notadequately compensate for irregularities in the substrate such as lackof parallelism, waviness, or warpage, or irregularities in the bondingtool. Accordingly, a plurality of pins which are individuallydisplaceable are advantageously employed to engage the compliant mediumat selected bonding areas. In this manner, the compliant mediumcompensates for localized irregularities while the pins are individuallydisplaced to compensate for irregularities between different bondingareas.

Bonds may also be made using ultrasonic energy by mounting the substrateon an anvil and vibrating the anvil to impart ultrasonic energy to thebonding sites. Thermal energy is advantageously applied just prior tothe ultrasonic energy to facilitate deformation of the compliant mediumabout the beam-lead devices or discrete leads. Engaging the compliantmedium at suitable bonding areas with individually displaceable pins tocompensate for irregularities between the different bonding areas hasthe same advantages set forth above.

THE DRAWINGS Understanding of the invention will be facilitated byreferring to the following detailed description of the severalembodiments, in conjunction with the accompanying drawings, wherein:

FIGS. 1A and 1B are side and end elevations, respectively, showing allparts in place for bonding a lead to a substrate by thermocompressionbonding in accordance with the invention;

FIGS. 2A and 2B are similar to FIGS. 1A and 18, showing all parts duringthermocompression bonding in accordance with the invention;

FIGS. 3A and 3B are similar to FIGS. 1 and 2, showing all parts afterthermocompression bonding is complete FIG. 4 is a side elevation of abeam-lead device positioned on a substrate;

FIG. 5 issimilar to FIG. 4 and shows the in place;

FIG. 6 is a side elevation of the assembly of FIG. 5 duringthermocompression bonding in accordance with the inventron;

FIG. 7 is a side elevation of the device of FIG. 4 after bondg I FIG. 8is a side elevation showing a beam-lead device on a substrate ready forultrasonic bonding in accordance with another embodiment of theinvention;

FIG. 9 is a side elevation of the assembly of FIG. 10 during ultrasonicbonding;

FIG. 10 is a side elevation showing all parts in place for ultrasonicbonding of a plurality of balled wire leads to a substrate in accordancewith another embodiment of the invention;

FIG. 11 is a side elevation showing the assembly of FIG. 10 duringultrasonic bonding;

FIG. 12 is a perspective view of a lead frame for a beamlead device ordevices for use in thermocompression bonding in accordance with theinvention;

FIG. 13 is a side elevation of a jig for use in wide area compliantbonding in accordance with the invention;

FIG. 14 is a plan view of the jig shown in FIG. 13;

FIGS. 15 and 16 are side elevations showing the jig of FIG. 13 used formultichip bonding; and

FIG. 17 is a partial perspective view of a machine capable of makingeither thermocompression or ultrasonic bonds in accordance with theinvention.

compliant medium FIGS. I-3 illustrate bonding of a single lead to asubstrate. An insulating substrate having a metallic land area 12 on thesurface thereof is placed on a rigid support (not shown). A lead 14 isplaced over land area 12 at the desired bonding point. For purposes ofillustration, it can be assumed that substrate 10 is a high aluminaceramic, and land area 12 and lead 14 are both gold. The compliantmedium is in the form of a wire 16 of a film-forming metal such asaluminum. A heated ram 18 initially clamps the workpieces to the supportand, as pressure is applied, wire 16 and lead 14 commence to deform, asshown in FIG. 2. In particular, the line of contact 20 between the twopieces becomes a zone of contact 22, and bulges 24 appear on theunconfined edges of lead 14. At the same time, wire 16 deforms aroundlead 14. When bonding is complete, as shown in FIG. 3, the initialbulges have been deformed into area 26, and wire 16 has deformed so asto completely cover the entire bond area on both workpieces. The flow ofthe lead metal in the area 26 against the land metal 12' contributes tothe quality of the bond.

The wire 16 will not itself bond to the workpieces because of the toughoxide film on its surface. Since film-forming metals (aluminum, nickel,titanium, tantalum, etc.) always have such oxide films and the thicknessthereof can be readily controlled by anodizing, they are preferred asthe compliant medium. Other materials can be employed and partingmaterials used to prevent bonding of the medium to the workpiece, butparting materials will of course be avoided where they might present acontamination problem.

Since gold is a relatively soft metal, compared to aluminum, one mightthink that the wire 16 would cut right through lead 14 or mash itcompletely, but this is not the case. Successful bonds of gold leadshave even been made using nickel as the compliant medium, which is evenharder than aluminum. Of course, when selecting a compliant medium,persons skilled in the art will obviously avoid metals and alloys thatwould not deform under the bonding conditions.

Bonds produced in the foregoing manner have been determined to besuperior to bonds made by conventional ultrasonic and thermocompressiontechniques. This superiority is both statistical (i.e., the number ofgood bonds made per thousand) and absolute (i.e., bond strength in ashear-peel test). While not wishing to be bound to any particular theoryof operation, it is believed that the reason for this superiority can beexplained by reference to some of the fundamentals of ordinarythermocompression bonding.

It has been previously determined that, for a given ram pressure (i.e.,load), there is a satisfactory range of bonding temperatures that willproduce a good bond. Conversely, for a given bonding temperature, thereexists a range of loads that will produce a good bond. This assumes aconstant bonding cycle. As would be expected, the higher the load thelower the satisfactory temperature range, and vice versa. Expresseddifferently, it could be said that there is a range of total bondingenergy which will produce a good bond, and this can be divided betweenmechanical and thermal energy in any desired way. If insufficient totalbonding energy is applied, the lead will not adhere to the substrate(i.e., in a pull test, separation will occur at the interface). If toomuch bonding energy is applied, the lead will be killed (i.e., in a pulltest, the lead will break). Prior workers have studied the geometry ofvarious bonding tips at great length to overcome the killing" problem,but to little avail.

In bonding with a compliant medium in accordance with the presentinvention, it has been determined that the upper limit of total bondingenergy that produces a good bond is raised substantially. Thus, theproblem of killing" a bond is substantially reduced. This is in partexplained by the fact that, to a lesser or greater extent, the compliantmedium is deforming rather than the workpiece, but this fact does notexplain the high strength of bonds produced. The actual mechanism ofbonding at the interface is believed to be diffusion, regardless of thetype of bonding employed. Diffusion is a time and temperature dependentprocess. The load-temperature relations discussed above assume aconstant bonding time, but with compliant medium bonding, where killing"the bond is not such a problem, a slightly longer bonding time can beemployed. This allows for greater diffusion at the interface, and astrong and better bond results. It is to be emphasized that theinterrelation between all of the various parameters of bonding is acomplex one, and the foregoing is offered only as a reasonableexplanation. The same fundamentals apply to ultrasonic bonding as tothermocompression techniques, but the mechanisms at work are quitedifferent. For example, heat is generated by both internal and externalfriction and hysteresis, in addition to any external sources that mightbe used. However, the foregoing explanation is also reasonable whereultrasonic energy is employed.

FIGS. 4-7 illustrate the bonding of a beam-lead integrated circuitdevice to a substrate. As shown in FIG. 4, the device comprises asilicon chip 28 having gold leads 30 issuing therefrom. It rests on asubstrate 32 having metallic land areas (not shown) under each lead.

As shown in FIG. 5, a hollow preform or lead frame 34 is placed overleads 30 and around device 28. Preform 34 extends substantially abovethe top of device 28 so that, during bonding, the hot ram will not pressupon device 28. Many such devices and particularly the more simple beamlead transistors, have substantial structural strength, and thecompliant medium can be caused to deform around the entire device andthe leads, thus eliminating the need for a hollow preform 34. This hasthe further advantage of eliminating any possibility of bending orbugging of the device, although this has not been a problem when bondingwith a hollow, compliant preform.

As illustrated in FIG. 6, a hot ram 36 is pressed down on the assembly,causing deformation of preform 34 and leads 30 in the same manner asdescribed hereinabove in connection with FIGS. l-3. It will be notedthat preform 34 deforms in exact compliance with the leads even whenthey are very closely spaced. FIG. 7 illustrates the bonded device afterremoval of the preform.

The extent of deformation of the leads during bonding is apparently afunction of the geometry of the compliant medium and the physicalproperties of the materials, more than anything else. FIGS. I-3 and 4-7illustrate two shapes of a compliant medium and two somewhat differentlead deformations. Where the compliant medium is a sheet which coversessentially the entire lead right up to the device, bonds are made withlittle or not visible deformation of the lead. The obvious, if notentirely satisfactory, explanation for this is that the energy couplefrom the source of the interface is, relatively, a broad area one, and agood bond is made with little deformation other than at the interface.In the bonding of beam-lead devices, it is preferred to use a solidsheet of the compliant medium which covers the entire device and theleads, when the device is strong enough. Ram pressure is appliedoverall, the medium deforms around the device and the leads, and makesgood bonds. Any tendency toward bugging" is manifestly impossible, sincethe device and the leads are subjected to the same forces.

The foregoing can be illustrated by a specific example of the bonding ofa l6-lead beam-leaded device to the Au/Ti land areas on a glasssubstrate. The compliant medium was 2024 aluminum 0.005 in. thick with asquare 0.0535 in. hole punched therein. The device was positioned on thesubstrate and the aluminum was placed thereover, the hole just fittingover the body of the device. The ram was 7 l 8 stainless with a flat,Inconel tip heated by a I50 watt cartridge heater. Bonding was carriedout for 1.5 seconds with a total ram pressure of about 48 pounds (3pounds per lead) at a temperature of 400 C. Lateral deformation of thebeams due to bonding was less than 10 percent. After bonding, the devicecould not be blasted loose with 400 psi compressed air. When a sharprobe was used to shear the device from the substrate, all 16 leads brokeoff and remained bonded to the substrate.

In general, it has been found that successful thermocornpression bondscan be made in accordance with the invention at temperatures in therange of 350 500 C, bonding cycles of l to even seconds, and at a ramforce of 50 pounds. It will be appreciated, however, that all of theseparameters are related. At lower temperatures, for example, longercycles are in order, and vice versa.

FIGS. 8 and 9 illustrate ultrasonic bonding with a compliant medium. Inthis embodiment a support or table 38 is provided which is connected toan ultrasonic horn for vibration in a direction parallel to the uppersurface. It is convenient to provide a slight depression 40 in the uppersurface of support 38 which conforms to the size of the substrate towhich leads are to be bonded. A substrate 42 is placed in thisdepression and, as shown in FIGS. 8 and 9, a beam-lead device 44 ispositioned thereon. A plunger or clamp 46 has a tip 48 which is acompliant medium capable of deforming around the device and clamping allthe leads, regardless of size differences, securely to substrate 42.Plunger 46 can be hydraulic, cam actuated, solenoid actuated, or othersuitable means can be employed.

Ultrasonic energy is applied and causes support 38 to vibrate in thedirection shown by the arrow in FIG. 9, i.e., parallel to the surface.The bond-is made in the conventional ultrasonic manner.

It has been heretofore disclosed that heat can be advantageously appliedduring ultrasonic bonding to facilitate deformation of the compliantmedium about the devices. The application of heat through a conventionalultrasonic bonding tip creates problems, however, in that the sonicproperties of the tip are in part temperature dependent. This problem iseliminated in the present invention because the heat can be appliedthrough plunger 46 and compliant medium 48.

The ultrasonic bonding of two balled wire leads to land areas on asubstrate is shown in FIGS. 10 and 11. The substrate 42 has twoconductive land areas 50 and two balled leads 52 are positioned thereon.It will be noted that leads 52 differ substantially in size. In thisinstance discrete, springloaded plungers 54 may be employed without thecompliant member 48, each plunger 54 accommodating one lead and clampingit firmly to the substrate. Bonding is carried out in the same manner asdescribed above in connection with FIGS. 8 and 9, and heat isadvantageously supplied through plungers 54. It will be appreciated thatunless the plungers 54 are provided with a compliant medium, theembodiment of FIGS. 10

and 11 is suitable only for bonding wire leads or relatively largedevices, and could not be used for bonding very small beam-lead orintegrated circuit devices.

FIG. 12 illustrates the use of a compliant medium, particularly afilm-forming metal, as a lead frame for one or more discrete beam-leaddevices. A rectangular frame 56 having an aperture 58 is provided, intowhich the device 60 is placed through the bottom, the leads 62 of device60 being lightly adhered to the underside of frame 56 by use of anadhesive. Altematively, aperture 58 may be sized so that the body 60fits snugly therein and is frictionally retained. Indexing marks 64 areprovided on the outside of frame 56 and are designed to register withcorresponding marks on the substrate to which the device is to beattached. Similar marks (not shown) on the underside of frame 56 willfacilitate the accurate placement of the device within the frame. -Inthis manner, proper registration of each lead with its correspondingland area on the substrate in considerably simplified. The dotted lines65 show how frame 56 may be part of a much larger frame holding aplurality of devices 60. As noted hereinabove, the lead frame may takethe form of a long ribbon or tape of the compliant medium. Also,indexing may be accomplished with optical equipment by having smallholes in the tape or lead frame. As will be appreciated, the lead framemay be used to position a plurality of devices relative to a substratefor multichip bondmg.

FIGS. 13 and 14 are elevation and plan views, respectively, of a jigsuitable for multichip bonding or for multiple lead bonding where theleads are spaced over a relatively large area. A plate 66 is providedwith apertures 68 for attachment in exact registry to pins on a bondingmachine. A set of apertures 70 is provide equal in number to and spacedfor registry with widely spaced leads or with a plurality of spaceddevices to be bonded. A pin 72 having a stop-key 74 near one end and acollar 76 near the other is placed in each aperture 70 with a spring 78partially compressed between collar 76 and the underside of plate 66,stop-key 74 serving to retain each pin 72 in position. When the jig isemployed to bond a plurality of devices, a compliant medium is used inconjunction with the plI'lS.

Plate 66 is mounted in a vertically movable fixture in a bonding machineand, when the devices 60 are positioned on a suitable substrate on thesupport, the fixture is lowered. The tips of pins 72 engage theindividual devices through a compliant medium and, as the fixture islowered still more, springs 78 are further compressed, exerting throughpins 72 a clamping force sufficient to efifect bonding upon theapplication of heat and/or ultrasonic energy. If desired, thermal energymay be applied by passing a hot gas around the bond regions instead ofheating the pins directly.

Referring now to FIGS. 15 and 16, in multichip bonding where there areirregularities in the substrate 42 such as warpage (FIG. 15), lack ofparallelism (FIG. 16) and waviness, it is necessary to compensate forsuch irregularities in the substrate as well as irregularities in theleads and/or land area, e.g variations in thickness, etc. Irregularitiesbetween bonding areas on the substrate may be compensated for by thepins 72 and localized irregularities in the leads, land areas andsubstrate are compensated for by the compliant medium, preform 42 andlead frame 56. In this manner, multichip bonding becomes highlypractical and permits any number of devices to be bonded simultaneously.

In FIG. 15, a substrate 42 is illustrated which is warped. For purposesof illustration, the warpage is greatly exaggerated. As will beappreciated, if a single tool were employed to engage the compliantmedium at each bonding site, the tool would first engage the preform 34which is on the left and would apply excessive force to that area of thesubstrate thereby possibly fracturing the substrate whereas insufficientpressure to effect a bond would be applied to the preform 34 which is onthe right. By employing pins 72 which are individually displaceable, thepin .72 engaging the preform 34 which is on the left is urged againstits associated spring 78 to permit the jig to continue to advance tobring the pin 72 on the right into engagement with the preform 34 whichis on the right. In this manner, the pins 72 are permitted relativedisplacement to compensate for irregularities between bonding areas onthe substrate. The compliant medium, preform 34, compensates forlocalized irregularities in the leads, land areas and substrate asdiscussed hereinbefore. Bonding energy can be applied by ultrasonicallyvibrating the substrate and/or heating the pins 72. As will beappreciated, any suitable configuration for the compliant medium can beused.

In FIG. 16, a substrate 42 is illustrated which in nonparallel, i.e.,tapered. The degree of nonparallelism is also exaggerated forillustrative purposes. As in the embodiment of FIG. 15, if a single toolwere employed to engage the compliant medium at each bonding area, thetool would first engage the lead frame 56 above the left-hand device andwould apply excessive force to that area of the substrate therebypossibly fracturing the substrate whereas insufficient force to effect abond would be applied to the lead frame above the right-hand device. Byemploying individually displaceable pins, these irregularities betweenbonding areas on the substrate may be compensated for as set out above.The compliant medium, lead frame 56, compensates for localizedirregularities in the leads, land areas and substrate as discussedhereinbefore. Bonding energy can be applied by ultrasonically vibratingthe substrate and/or heating the pins 72. As will be appreciated, anysuitable configuration for the compliant medium can be used.

Also, in the embodiments of FIGS. 15 and 16, the pins 72 areconveniently permitted sufficient lateral displacement in the jig tofacilitate displacement of each pin into parallelism with the compliantmember.

It is usually desirable to employ a compensating base to support thesubstrate during bonding. An suitable compensating base may be employedsuch as those disclosed in US. application, Ser. No. 753,830, filed Aug.16, 1968, by R. H. Cushman and assigned to Western Electric Company,Incorporated.

FIG. 17 is a simplified perspective view of a bonding machine suitablefor use in compliant bonding.

With reference to FIG. 17, a base 100 is integral with a back portion102 which, together, form the support for the machine. A generallyU-shaped arm 104 (shown partially) exte'nds outwardly from the back 102and supports a suitable binocular microscope (not shown) for use by theoperator in positioning the various parts. Base 100 has provided thereona rigid table 106 on which there rests a plate 108 which is coupled toan ultrasonic horn 110 adapted to vibrate plate 108 in the horizontalplane. The ultrasonic energy source is conventional and is not shown. Asecond plate 112 is screwed onto plate 108 by means of four screws 114.Plate 112 is provided with a central depression 116 on the top surfacethereof adapted to contain and retain a specific substrate. The reasonfor providing separate plate 112 is so that variously sized substratesor circuit boards can be easily accommodated.

An upright member 118 is centrally located against back 102; this isprovided for the mounting of the vertically movable portions of themachine. Member 118 has a rack 120 on the forward vertical surfacethereof which engages a pinion or pinions (not shown) on the verticallymovable elements, much in the same manner as the barrel of a microscopeis raised and lowered on its frame.

For thennocompression bonding, a hydraulic or solenoid actuated rammechanism 122 is mounted on member 118. Ram mechanism 122 has adownwardly extending ram 124 with a replaceable tip 126. The reason forhaving tip 126 is, again, to accommodate variously sized devices, anddifferent types of tips. Thus, tip 126 may be of a plasticallydeformable film-forming metal, it may be apertured, it may be a fiatpiece of molybdenum (i.e., where a lead frame is employed), or it may bea suitable fixture for retaining a jig of the type illustrated in FIGS.13 and 14. Coarse and fine adjustments 128, 130 are provided forpositioning ram 124 prior to bonding. A dial 132 indicates ram pressureand a dial 134 indicates ram temperature. Power necessary for actuatingand heating the ram is provided via line 136. Other controls (not shown)are provided as required.

For ultrasonic bonding in accordance with the invention, ram mechanism122 is replaced by fixture 137. This also has a pinion gear or gears(not shown) and is adapted to be mounted on rack 120 on member 118.Fixture 137 has a simple frame 138 with an aperture 140 having anannular shoulder 142 therein. Aperture 140 and shoulder 142 are adaptedto contain and retain a jig such as is illustrated in FIGS. 13 and 14.Threaded posts (not shown) are provided on shoulder 142 to register withthe apertures (68, 82) of the jig so that the latter can be screweddown.

The substrate is placed in depression 116 and the device (or leads) ispositioned thereon. The operative element either ram 124 or fixture 137is then lowered to engage the assembly, and bonding energy is suppliedby either ram 124 or horn 110. In either case, all of the leads arebonded simultaneously, and bonding is both quick and reliable.

It will be understood that various changes in the details, steps,materials and arrangements of parts, which have been herein describedand illustrated in order to explain the nature of the invention, may bemade by those skilled in the art.

What is claimed is:

l. A jig for clamping a multi-leaded device to a substrate for bondingthereto comprising:

an apertured plate, the apertures of said plate corresponding in numberand position to the leads of said device;

a pin slidably mounted in each said aperture for transmitting a clampingforce to retain one of said leads;

spring means engaging each said pin and said plate and tending to forceeach said pin in a direction axially along the associated aperture toprovide said clamping force; and

means associated with each said pin for retaining said pin in saidaperture.

2. A device for compliant bonding at least two first workpieces towidely spaced bonding sites on a second workpiece, said devicecomprising:

a compliant medium associated with each bonding site for engaging saidworkpieces, and

means for simultaneously applying bonding pressure to said compliantmedium at all of the bonding sites with the pressure applied at eachindividual bonding site being independent of the pressure applied ateach other bonding site so as to compensate for workpiece irregularitiesbetween said bonding sites while compliantly bonding each firstworkpiece to said second workpiece.

3. The device of claim 2 wherein the first workpieces are beam-leaddevices.

4. The device of claim 3 wherein the means for independently applyingbonding pressure to each bonding site is a plurality of individuallydisplaceable pins.

5. The device of claim 2 wherein the first workpieces are discreteleads.

6. The device of claim 5 wherein the means for independently applyingbonding pressure to each bonding site is a plurality of individuallydisplaceable pins.

7. A device for compliantly bonding at least two first workpieces towidely spaced bonding sites on a second workpiece, said devicecomprising:

a compliant medium associated with each bonding site for engaging eachfirst workpiece;

a plurality of individually mounted pins, each pin being associated witha bonding site on said second workpiece; and

means for applying sufiicient energy independently through each of saidindividually mounted pins and said compliant medium to each respectiveassociated bonding site to compliantly bond each first workpiece to saidsecond workpiece while compensating for workpiece irregularities betweensaid bonding sites.

8. The device of claim 7 wherein each pin is spring biased to permitindividual displacement of each pin to compensate for workpieceirregularities between bonding sites.

9. The device of claim 8 wherein a compliant medium is secured to eachpin.

10. The jig of claim 1, further comprising:

a compliant medium engaging the extremity of each pin furthest alongsaid axial direction.

11. The jig of claim 10 wherein the compliant medium is secured to eachpin.

12. The jig of claim 10 wherein each of a plurality of independentmembers composed of the compliant medium engages an extremity of adifierent pin.

1. A jig for clamping a multi-leaded device to a substrate for bondingthereto comprising: an apertured plate, the apertures of said platecorresponding in number and position to the leads of said device; a pinslidably mounted in each said aperture for transmitting a clamping forceto retain one of said leads; spring means engaging each said pin andsaid plate and tending to force each said pin in a direction axiallyalong the associated aperture to provide said clamping force; and meansassociated with each said pin for retaining said pin in said aperture.2. A device for compliant bonding at least two first workpieces towidely spaced bonding sites on a second workpiece, said devicecomprising: a compliant medium associated with each bonding site forengaging said workpieces, and means for simultaneously applying bondingpressure to said compliant medium at aLl of the bonding sites with thepressure applied at each individual bonding site being independent ofthe pressure applied at each other bonding site so as to compensate forworkpiece irregularities between said bonding sites while compliantlybonding each first workpiece to said second workpiece.
 3. The device ofclaim 2 wherein the first workpieces are beam-lead devices.
 4. Thedevice of claim 3 wherein the means for independently applying bondingpressure to each bonding site is a plurality of individuallydisplaceable pins.
 5. The device of claim 2 wherein the first workpiecesare discrete leads.
 6. The device of claim 5 wherein the means forindependently applying bonding pressure to each bonding site is aplurality of individually displaceable pins.
 7. A device for compliantlybonding at least two first workpieces to widely spaced bonding sites ona second workpiece, said device comprising: a compliant mediumassociated with each bonding site for engaging each first workpiece; aplurality of individually mounted pins, each pin being associated with abonding site on said second workpiece; and means for applying sufficientenergy independently through each of said individually mounted pins andsaid compliant medium to each respective associated bonding site tocompliantly bond each first workpiece to said second workpiece whilecompensating for workpiece irregularities between said bonding sites. 8.The device of claim 7 wherein each pin is spring biased to permitindividual displacement of each pin to compensate for workpieceirregularities between bonding sites.
 9. The device of claim 8 wherein acompliant medium is secured to each pin.
 10. The jig of claim 1, furthercomprising: a compliant medium engaging the extremity of each pinfurthest along said axial direction.
 11. The jig of claim 10 wherein thecompliant medium is secured to each pin.
 12. The jig of claim 10 whereineach of a plurality of independent members composed of the compliantmedium engages an extremity of a different pin.